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Forum: Analog Circuits Thyristor as DC switch - resitance to high


von Hans L. (haled)


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Hi everyone,
I am currently  building a remote controlled switch that is cutting the 
power line of a device. The problem hereby is that I have no access to 
ground so the switch needs to be powered by the very same cable it is 
cutting/switching.
Until now I managed to make this "two-wire-solution" work with a MCU and 
a thyristor as you can see in the picture. Hereby when the power supply 
is activated the current flows trough the MCU as the thyristor is still 
high-resistance. Once the MCU triggers the thyristor it becomes 
low-resistance so the switch is "ON". At the same time the MCU turns off 
as it only gets low voltage which is ok as the Tyristor stays in 
conductive mode as long as current flow is high enough. The system gets 
reset by cutting the power supply which is exactly the behavior I want 
to accomplish.
My problem is, that the thyristor has a relatively high resistance in 
conductive mode and I don't know how to find a thyristor with minimum 
resistance and what this minimum value would be.
Maybe there is also an option to use a relay and have the same 
functionality as with the thyristor? Ideally the switch would work for 
low and higher current devices up to 15 ampere. The power supply is 12V.
I hope I could describe my problem relatively clear.
Thanks a lot :-)

von A-Freak (Guest)


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Unfortunately, a thyristor has always at least about 1,2V drop across 
two forward bieased PN junctions.

The only idea i could think about that has much lower voltage drop would 
be a kind of latching relay that has a very low resistance coil in 
series with the load, some kind of mechanical thyristor.

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